DJRas
Member
But, Are they in balance only because the BMS has LOWERED all the other cells to match the "out of balance" one?
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Wiki Sudden Loss Of Range With 2019.16.x Software
- Thread starter Dutchmeeuw
- Start date
DJRas
Member
Is 33mv excessive?
Attachments
Can Tesla dial how much current goes to a given car, at a given SC, independent of what software is on board the car? IOW, can the chargers, themselves, discriminate? Over VPN, I assume Tesla sees real time super charging, but don't estimate they are simultaneously dialing the KW rate (to some algo, or otherwise). TIA
jaitch
Member
Do you have any more info on this? Eg where can I find how much cell imbalance is acceptable/normal under heavy discharge. On my P90DL I notice 0.2 V cell difference at 1500 + amps battery current. Under regen conditions cell difference shows 0.8 V. (Some cells showing reduced voltage under regen (3.2 V) vs high discharge (3.8 V) seems a little odd to me but I am learning this stuff! I thought owning a Tesla was going to lead to an easy car life!).
Thanks
James
One problem is that there's some latency in reading cell voltages - you don't read them all at once, it takes multiple CAN bus messages to get all cell voltages. You'd need to maintain continuous load/regen during the cycle to get accurate readings of the cell voltages under identical conditions.
I see the same thing, but even more drastic than yours. My taper crosses 36kW at 50%. There’s another thread over here: 2019 Supercharging Speed Update Nerfed Overall Charge Times
lightningltd
Member
You are seeing what I am seeing. I supercharge often and HAD a 3% range loss at 134,000 miles. Now it is MUCH MUCH more loss:
2013 S85 Battery revision B
New: 265 miles Rated Range (100%)
Pre update: 256 Miles Rated Range (96.60% from new) (3.4% range loss from new)
Post Update (suddenly): 217 Rated Miles (84.77% from pre update)(15.23% loss from pre update) (81.88% from new) (18.11% loss from new)
The fact that it is affecting some with the same part numbers and charging habits and not others is looking to me like a clear defect in materials or workmanship.
Can you get the data from your unaffected friend?
I agree with you - I thought that owning Tesla is a trouble free excersise but the more I dig the more interesting it becomes to own as its constantly teaching me new skills. My hobby background for past 2 decades is ICE engine tuning and hacing (yes, literally using dissassembler and rewriting firmware to various engine controller units) so I am already afraid that this becomes yet another hacking project for me... even though I promised to my wife that never again...
But then to answer to your question - Open Circuit voltage is not a good measurement of SoC and what we really want is SoC balance between cells. Closed circuit is more accurate but like outlined here earlier in the post with Tesla early patent there may be numerous reasons for triggering the "sudden loss of range" condition. I just started reading it to understand better how Tesla detects "fault conditions". Reading this and other relevant patents should give us a fair starting point to understand the Tesla thinking. The regen condition of 0.8V for (I guess) 50kW is a fair amount that could well trigger the condition.
Let me come back after having read the patent to avoid second guessing.
Here is what I learned from briefly reading the patent without analyzing it too much. In overall the BMS has a preconfigured set of parameters that the BMS uses to set a fault flag that modifies the charge parameters (possibly e.g. the max cell voltage).
When I talked earlier about detecting imbalance of cells I did not mean the actual cell voltages as likes someone said that OCV is a poor prediction of SoC. Rather when talking about imbalance of cells we need to take into account several possible algorithms.
The figures 3-8 in the patent demonstrate the trigger conditions. I am not an expert of lithium chemistry but someone who has that bacground can propably analyze the causes for each of these different conditions. My bet is that after the recent battery fires they just made the detection limits way more tight.
Even though the fault flag is set the patent lists several false positives like: Note that with respect to decreasing voltage, this method monitors for false trips due, for example, to (i) step change from one CC level or CP level to another, (ii) reduction in charge rate due to grid power or charger power limits in the presence of an HVAC load for example, (iii) external heating of the battery causing a reduction in impedance, or (iv) reduction in impedance at a rate which causes the loaded voltage to fall more quickly than the OCV rises.
My second bet is that due to the recent fires the newly imposed detection limits were not really tested and hence most likely yielding a fair amount of false positives. Like someone here said already "we are likely to see restored ranges in the future". Regardless of the outcome the Tesla customer communications is a real bummer - to me its like any typical engineering company with lack of ability to communicate whats important for customers...
Here is a repost of the link to the patent for the curious minds: https://patentimages.storage.googleapis.com/d4/c7/2b/48b50249e2c13e/US8866444.pdf
And below are the conditions we should start looking for to see if its a false positive or a real concern.
Methods 1 and 2 above (i.e., decreasing Voltage during charge and increasing current during CV charge) can be mea
Sured during any charge cycle that begins with V<V, and deltaT<(deltaT), where deltaT is the maximum difference
in temperature between the cells throughout the battery pack and the ambient temperature and (deltaT), is the maximum acceptable difference in temperature that would affect a change in Voltage or current during charging, this value being
determined through testing and contained in a look-up table. The battery-management system verifies that the charge cur
rent has not decreased or been interrupted, and that no addi tional loads have been introduced (i.e. HVAC) before indicat
ing a hazardous condition.
Methods 3 through 7 use time or capacity measurement. For methods 3 and 4, a time counter can be used to determine
if the battery has been charging longer than the time indicated in a look-up table for a pack of that capacity and state of
charge. This look-up table may be compiled from pack data, as well as from resistance measurements and cycling data
from cells at end-of life. These measurements also require that deltaT<(deltaT).
For method 5, the self-discharge rate of the pack can be measured and compared with the self
discharge rate for a cell of that capacity without an internal cell short present (from a look-up table). This can be mea
Sured using Voltage measurements over time, or, if a bleed circuit is present, it can be measured by determining the
amount of Ah passed through the bleed circuit to balance the series blocks of cells. These methods take into consideration
shallow and full charges, as well as SOC inaccuracy.
Method 6 (charge efficiency) is similar to method 5 in that it measures the amount of self-discharge. This method also
requires that any temperature, rate, and cutoff Voltage differ ences between charge and discharge are accounted for. If an
internal-cell short is present, the charge capacity will increase (some current is going through the short) and if the short is
maintained the discharge capacity will decrease relative to a cell without a short. The ratio of the discharge to the charge
capacity should be 1 for a fully reversible cell without shorts or side reactions. This value is typically ~99.97 or higher for
new cells without shorts. For a cell with an internal short, this value may be ~70% or lower. A low-end limit value is deter
mined through testing for the cell in use and this value will be included in a look-up table for the battery management sys
tem.
Method 7 may be the most simple to implement for some applications, especially in a large battery pack Such as the
type of pack that might be used in an electric vehicle. This method measures the total charge passed to the pack, module,
or parallel brick. If the total charge passed exceeds the expected charge capacity from the initial to final state of
charge (SOC), then the additional charge may have been dissipated through internal shorts. In a vehicle battery, the
capacity is continuously monitored in order to estimate remaining range. The calculated Ah capacity (CAC) is moni
tored as the packages, enabling this method to be used throughout the life of the battery pack. Say for example that a
100 Ah battery pack is assembled and it is at 20% SOC initially, or 20 Ah of energy is available in the pack. This
example pack contains cells with internal shorts and takes 130 Ah (an additional 110 Ah) to reach full pack voltage. This
means that 30 Ah were dissipated through internal cell shorts and caused the pack to heat up, potentially creating a hazard
ous condition. By comparing the total charge passed to the expected value, this method may be used to interrupt charge,
potentially before a hazardous condition can occur. Method 7 is doubly useful in that it can also be used as another layer of
protection against pack overcharge, a highly hazardous con dition should it occur.
Method 8 involves a real-time measurement of the impedance of parallel bricks of cells, and potentially also series
strings of cells. This measurement is continuously made during pack operation to estimate available power using a com
bination of Voltage and current measurements. During charge, these measurements are typically not made. However,
Some embodiments of this invention propose use of a continuous estimation of battery impedance to detect an internal
short. For a given SOC, the expected impedance can be kept in a look-up table. If the impedance at that SOC is lower than
the threshold value, it may indicate that an internal cell short has formed. This would capture the case of a decreasing
US 8,866,444 B2 Voltage during CC or CP charge as well as an increase in current during CV charge. As indicated above, any additional load on the battery pack or change in temperature is properly accounted for.
Method 9 involves the direct measurement of a resultant increase in temperature due to an internal-cell short. The cell,
brick, and coolant temperature (refrigerant, water, air or another working fluid) is monitored continuously. If it
increases intemperature more rapidly and/or to a higher value than is expected for that charge condition, a hazardous con
dition is indicated and the charge is interrupted.
When I talked earlier about detecting imbalance of cells I did not mean the actual cell voltages as likes someone said that OCV is a poor prediction of SoC. Rather when talking about imbalance of cells we need to take into account several possible algorithms.
The figures 3-8 in the patent demonstrate the trigger conditions. I am not an expert of lithium chemistry but someone who has that bacground can propably analyze the causes for each of these different conditions. My bet is that after the recent battery fires they just made the detection limits way more tight.
Even though the fault flag is set the patent lists several false positives like: Note that with respect to decreasing voltage, this method monitors for false trips due, for example, to (i) step change from one CC level or CP level to another, (ii) reduction in charge rate due to grid power or charger power limits in the presence of an HVAC load for example, (iii) external heating of the battery causing a reduction in impedance, or (iv) reduction in impedance at a rate which causes the loaded voltage to fall more quickly than the OCV rises.
My second bet is that due to the recent fires the newly imposed detection limits were not really tested and hence most likely yielding a fair amount of false positives. Like someone here said already "we are likely to see restored ranges in the future". Regardless of the outcome the Tesla customer communications is a real bummer - to me its like any typical engineering company with lack of ability to communicate whats important for customers...
Here is a repost of the link to the patent for the curious minds: https://patentimages.storage.googleapis.com/d4/c7/2b/48b50249e2c13e/US8866444.pdf
And below are the conditions we should start looking for to see if its a false positive or a real concern.
Methods 1 and 2 above (i.e., decreasing Voltage during charge and increasing current during CV charge) can be mea
Sured during any charge cycle that begins with V<V, and deltaT<(deltaT), where deltaT is the maximum difference
in temperature between the cells throughout the battery pack and the ambient temperature and (deltaT), is the maximum acceptable difference in temperature that would affect a change in Voltage or current during charging, this value being
determined through testing and contained in a look-up table. The battery-management system verifies that the charge cur
rent has not decreased or been interrupted, and that no addi tional loads have been introduced (i.e. HVAC) before indicat
ing a hazardous condition.
Methods 3 through 7 use time or capacity measurement. For methods 3 and 4, a time counter can be used to determine
if the battery has been charging longer than the time indicated in a look-up table for a pack of that capacity and state of
charge. This look-up table may be compiled from pack data, as well as from resistance measurements and cycling data
from cells at end-of life. These measurements also require that deltaT<(deltaT).
For method 5, the self-discharge rate of the pack can be measured and compared with the self
discharge rate for a cell of that capacity without an internal cell short present (from a look-up table). This can be mea
Sured using Voltage measurements over time, or, if a bleed circuit is present, it can be measured by determining the
amount of Ah passed through the bleed circuit to balance the series blocks of cells. These methods take into consideration
shallow and full charges, as well as SOC inaccuracy.
Method 6 (charge efficiency) is similar to method 5 in that it measures the amount of self-discharge. This method also
requires that any temperature, rate, and cutoff Voltage differ ences between charge and discharge are accounted for. If an
internal-cell short is present, the charge capacity will increase (some current is going through the short) and if the short is
maintained the discharge capacity will decrease relative to a cell without a short. The ratio of the discharge to the charge
capacity should be 1 for a fully reversible cell without shorts or side reactions. This value is typically ~99.97 or higher for
new cells without shorts. For a cell with an internal short, this value may be ~70% or lower. A low-end limit value is deter
mined through testing for the cell in use and this value will be included in a look-up table for the battery management sys
tem.
Method 7 may be the most simple to implement for some applications, especially in a large battery pack Such as the
type of pack that might be used in an electric vehicle. This method measures the total charge passed to the pack, module,
or parallel brick. If the total charge passed exceeds the expected charge capacity from the initial to final state of
charge (SOC), then the additional charge may have been dissipated through internal shorts. In a vehicle battery, the
capacity is continuously monitored in order to estimate remaining range. The calculated Ah capacity (CAC) is moni
tored as the packages, enabling this method to be used throughout the life of the battery pack. Say for example that a
100 Ah battery pack is assembled and it is at 20% SOC initially, or 20 Ah of energy is available in the pack. This
example pack contains cells with internal shorts and takes 130 Ah (an additional 110 Ah) to reach full pack voltage. This
means that 30 Ah were dissipated through internal cell shorts and caused the pack to heat up, potentially creating a hazard
ous condition. By comparing the total charge passed to the expected value, this method may be used to interrupt charge,
potentially before a hazardous condition can occur. Method 7 is doubly useful in that it can also be used as another layer of
protection against pack overcharge, a highly hazardous con dition should it occur.
Method 8 involves a real-time measurement of the impedance of parallel bricks of cells, and potentially also series
strings of cells. This measurement is continuously made during pack operation to estimate available power using a com
bination of Voltage and current measurements. During charge, these measurements are typically not made. However,
Some embodiments of this invention propose use of a continuous estimation of battery impedance to detect an internal
short. For a given SOC, the expected impedance can be kept in a look-up table. If the impedance at that SOC is lower than
the threshold value, it may indicate that an internal cell short has formed. This would capture the case of a decreasing
US 8,866,444 B2 Voltage during CC or CP charge as well as an increase in current during CV charge. As indicated above, any additional load on the battery pack or change in temperature is properly accounted for.
Method 9 involves the direct measurement of a resultant increase in temperature due to an internal-cell short. The cell,
brick, and coolant temperature (refrigerant, water, air or another working fluid) is monitored continuously. If it
increases intemperature more rapidly and/or to a higher value than is expected for that charge condition, a hazardous con
dition is indicated and the charge is interrupted.
CuriousG
Active Member
Charged at low SoC today with 17 miles remaining. Very briefly ramped up to 105kW then ramped down rather quickly. My 90% remains the same after the sudden degradation of 23 miles within a month. Prior to that, degradation was about 10 miles total from new battery.
What, no sadness for me since I'm selling too?
Thought I had read this entire thread, but I missed that.
Ack.
Will you consider another tesla?
*
I believe this is crisis management time
A very big deal.
The wildfire potential of letting The Fire Burn
is Not simply the loss of a few individual customers
It is the effect on the circle of people around each customer.
Then they relate to their circle, hey you know the person I mentioned
who could never stop talking about the great Tesla...?
*
The extreme advocacy of a passionate user base starts working in reverse.
*
I was glad to see Elon's twitter storm, i have missed those.
He seems in better spirits
Hoped to see something about this.
If anyone has the rank to speak to the man, please do that.
It may be a minor issue amongst his many concerns.
No way to know what he even knows about it.
Keep the faith.
That article is old (2006) but states a lot of the things we have always heard about the batteries. What was really interesting was it says that they limit the voltage of the cells to 4.15 V instead of 4.2 V to prolong the battery life. Somewhere along the way Tesla obviously decided to push it to 4.2 V and now they may be trying to recover from that move.
Only 4.2 if you decide to charge to that. I've charged to 100% maybe 10 times in 4.5 years. Not very often but sometimes I have to have it. I've seen very little degradation probably because not only do I not charge high very often, when I charge to anything above 70% I don't let it sit more than an hour before using it. If I charge to 100%, I don't let it sit for more than a few minutes before using it.
Heck, I'd even be fine with:
1) Stern warning about charging above 95% whenever you do it.
2) Limiting the number of times within a time period how often you can go above 95%. Say no more than once a month.
3) Once you head over 95%, the car starts discharging immediately perhaps by running the AC to keep the batteries cool.
My drone batteries default setting is to start discharging from 100% within an an hour. You're not supposed to charge to 100% and store it that way.
1) Stern warning about charging above 95% whenever you do it.
2) Limiting the number of times within a time period how often you can go above 95%. Say no more than once a month.
3) Once you head over 95%, the car starts discharging immediately perhaps by running the AC to keep the batteries cool.
My drone batteries default setting is to start discharging from 100% within an an hour. You're not supposed to charge to 100% and store it that way.
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